Many products have foam resin disposed between a pair of pieces of sheet metal for a variety of purposes, such as providing a flexible connection between the pieces, supporting one of the pieces, preventing the transmission of noise between the pieces, preventing the pieces from striking each other, filling the space between the pieces, electrically and thermal insulating the pieces, and the like.
For example, in manufacturing the bodies of vehicles such as trucks, cars, and buses, a foam resin is disposed between a sheet metal roof panel and an underlying sheet metal bow or support for the roof panel. When making the body, an elongate ribbon of an expandable resin containing a heat activated blowing agent has been fastened by staples to a roof bow of sheet metal. Subsequently, the sub-assembly of the resin and bow is assembled in the body so that it underlies and is spaced from the roof panel. Thereafter, the body passes through an oven, such as a paint-baking oven, which heats the ribbon of resin sufficiently to activate the blowing agent which causes the resin to foam and expand so that it bears on the underside of the roof panel and fills the space between the bow and the panel. This supports the roof panel without the bow bearing directly on the panel and hence prevents transmission of noise and the bow and panel from striking each other.
However, in practice, the staples produce a non-uniform expansion of the resin foam which distorts or warps the roof panel and frequently, even causes an impression of the central portion of the staple to be clearly visible in an exterior surface of the painted roof panel. Attempts to manufacture this assembly without fastening the ribbon of resin to the bow before it is expanded also have been largely unsuccessful. It is difficult to handle and sub-assemble with the roof panel the bow and ribbon of resin as separate pieces when the ribbon is unsecured. Moreover, when unsecured, portions of the ribbon tend to shift or move with respect to the bow so that it is not located where desired when heated to activate the blowing agent and when heated expands unevenly which results in distortion of the roof panel and sometimes spots where there is inadequate foam resin to isolate the panel from the bow which results in highly undesirable noise or rattles when the vehicle is in use.